Hydraulic fracturing is a common stimulation technique used to enhance production of hydrocarbon fluids and gas from subterranean formations. In a typical hydraulic fracturing treatment, a fracturing fluid containing solid proppants is injected into the wellbore at pressures sufficient to create or enlarge a fracture in the reservoir. The proppant is deposited in the fracture and serves to hold the fracture open, thereby enhancing the ability of hydrocarbons to migrate from the formation to the wellbore through the fracture. Because well productivity depends on the ability of a fracture to conduct hydrocarbons from the formation to the wellbore, fracture conductivity is an important parameter in determining the degree of success of a hydraulic fracturing treatment.
The creation of reservoir “fines” during hydraulic fracturing has been reported to create problems. Most notably, fines are instrumental in reducing fracture conductivity. When proppant materials are subjected to reservoir closure stresses and are compressed together, fines are generated. Production of fines in the reservoir also often results in a reduction in reservoir permeability due to plugging of pore throats by the fines in the reservoir matrix.
Since the degree of stimulation afforded by the fracture treatment is dependent upon the propped width, it is important that the proppant exhibit resistance to crushing from the high stresses in the well. Improvements have been continuously sought to control and prevent the crushing of proppants at in-situ reservoir conditions. For instance, resin-coated proppant materials have been designed to help form a consolidated and permeable fracture pack when placed in the formation wherein the resin coating enhances the crush resistance of the proppant. The coating may further act as a tackifying agent to control fines from migrating into the proppant pack. The coating may be applied to the proppant by mixing proppant particulates with a resinous system and hardening the resin in-situ. Alternatively, a pre-coated proppant may be pumped into the formation with the fracturing fluid. Further, the proppant may be pumped into the formation and then consolidated with a curing solution which is pumped after the proppant material is in place.
Fines may further migrate during gravel packing Gravel packing is a sand-control method employed to prevent the production of formation sand. Gravel packing treatments are used to reduce the migration of unconsolidated formation particulates into the wellbore. Typically, gravel pack operations involve placing a gravel pack screen in the wellbore and packing the surrounding annulus between the screen and the wellbore with gravel designed to prevent the passage of formation sands through the pack. The gravel pack screen is generally a type of filter assembly used to support and retain the gravel placed during the gravel pack operation. Particulates known in the art as gravel are carried to a wellbore by a hydrocarbon or water carrier fluid. The carrier fluid leaks off into the subterranean zone and/or is returned to the surface while the particulates are left in the zone. The resultant gravel pack acts as a filter to separate formation sands from produced fluids while permitting the produced fluids to flow into the wellbore.
In some situations the processes of hydraulic fracturing and gravel packing are combined into a single treatment to provide stimulated production and an annular gravel pack to reduce formation sand production. Such treatments are often referred to as “frac pack” operations. In some cases, the treatments are completed with a gravel pack screen assembly in place, and the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In such a situation, the hydraulic fracturing treatment usually ends in a screen out condition creating an annular gravel pack between the screen and casing. This allows both the hydraulic fracturing treatment and gravel pack to be placed in a single operation.
To minimize the migration of formation fines, coated and/or uncoated particulates have further been used in gravel packing. While the use of resin coated proppants has been successful in minimizing the generation of fines during hydraulic fracturing and fine migration during gravel packing, such materials are known to erode oil and gas production equipment. There is an ongoing need to develop particulates exhibiting crush resistance that can be used as proppants and gravel for minimizing fines generation and fines migration, reduce proppant pack and gravel pack damage, and which are less eroding to oil and gas production equipment.
In addition to concerns arising from the creation of fines, the use of certain particulates used as proppants during hydraulic fracturing and sand control particulates have presented other challenges. One such concern is presented by the release of dust from those particulates carrying a positive or negative charge. For instance, with certain proppants, such as sand, dust is released during transport of the proppant as well as during usage of the proppant within the well. Recently, the release of dust from fracturing operations has come under close scrutiny as health concerns upon field workers and those within residential areas within the vicinity of on-shore fracturing has risen. There has not been a method developed to date which is specifically designed to reduce the release of dust from proppants. While resin coating of frac sand has been noted to decrease dust production, the addition of a resin coating doubles the cost of frac sand. In addition, the chemicals used to make the resins are not environmentally friendly. Lastly, the application of resin coating to frac sand requires the sand to be heated either by electricity or the burning of natural gas, both of which are costly. Alternative methods for reducing the generation of dust from charged particulates have thus been sought.